1. Field of the Invention
The present invention relates to a clutch cover assembly. More specifically, the present invention relates to a clutch cover assembly that presses a friction member of a clutch disc assembly against the flywheel of the engine and releases the friction member from the flywheel.
2. Background Information
A clutch cover assembly is generally attached to a flywheel of an engine to transmit a driving force from the engine to a transmission. The clutch cover assembly is mainly composed of a clutch cover fixed to the flywheel, a pressure plate provided to sandwich a friction member of a clutch disc assembly between itself and the flywheel, and a diaphragm spring provided to press the pressure plate toward the flywheel. The diaphragm spring has an annular elastic portion and a plurality of lever portions extending radially inward from an inner periphery of the annular elastic portion. The diaphragm spring has a pressing function to press the pressure plate and a lever function to release the pressure toward the pressure plate.
Pressing load characteristics of a clutch cover assembly will now be described. The pressing load characteristic shows a use area of the diaphragm spring as a pressing load in load characteristics. For example, as shown in FIG. 6, in the pressing load characteristic 20, an effective use area (a margin of wear) of the clutch cover assembly is an area in which a certain magnitude of the pressing load is obtained (from a set line 25 of a new product to a wear line 26 where the friction member is worn to the wear limit).
Next, the release load characteristic of the clutch cover assembly will be described. The release load characteristic shows a relationship between the operation amount (the stroke of lever) of a release lever and the load that is applied to the tips of the release lever (release load). For example, as shown in FIG. 9, the release load characteristic 60 has a first portion 61 that linearly increases from the lever stroke zero, a second portion 62 that gradually decreases, and makes a peak at the load balance point 63 when the first portion 61 and the second portion 62 contact. The first portion 61 indicates lever rigidity of the diaphragm spring, and the second portion 62 corresponds to changes from the set line toward the right side in figures in the pressing load characteristic.
Pressing load characteristic 20 increases, as shown in FIG. 6, at a constant rate as displacement magnitude of the diaphragm spring increases from zero, but it gradually decreases after the deflection amount crosses a certain point (peak point), and gradually increases after the deflection amount crosses another point. Accordingly, a peak 21 (a portion convex upward) in the effective use area is formed, and as the wear of friction member increases (the set line shifts leftward in figures), the pressing load increases. In other words, when the friction member is worn, the release load increases and it is difficult to avoid the increase of the clutch pedal pressure.
Therefore, as a structure to cut the peak in the pressing load characteristics, peak cut clutches have been known that use elastic member to generate a load to counteract the load of the diaphragm spring when the friction member is worn. In the peak cut clutch, the opposite peak in the characteristic of the elastic member is superimposed onto the peak in a characteristic of the diaphragm spring so that a flat portion is obtained in the composite load.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved clutch cover assembly. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.